<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <script>
        let numbers = [1, 2, 3, 4, 5];
        let find_el = numbers.find(n => n > 3);
        let find_index = numbers.findIndex(n => n < 3);
        console.log(find_el);
        console.log(find_index);

        let a = [1, 2, 3].includes(2); // true
        let b = [1, 2, 3].includes(4); // false
        let c = [1, 2, NaN].includes(NaN); // true
        console.log(`${a}----${b}-----${c}`);
    </script>
</head>

<body>

</body>

</html>